Effect of Nanoparticle Shape on the Oxygen Reduction Reaction Activity of PtNiFe Nanocatalysts

PtNiFe octahedra, nanocubes, polyhedra, and cuboctahedra were prepared using alkyl phosphonic acid and oleylamine as surfactant molecules. The synthesis route affords controlling PtNiFe nanostructures by changing the molar ratio of alkyl phosphonic acid/oleylamine ( R m ). The different R m values induce specific crystal facet–surfactant bindings on the growth seed, yielding the nanocrystals of various shapes. Both experimental and statistical results reveal that higher R m results in the formation of shapes rich in {100} facets, such as nanocubes and cuboctahedra. On the contrary, lower R m causes the formation of shapes rich in {111} facets, such as octahedra and polyhedra. The theoretical works determine a preferential adsorption of alkyl amine molecules on the PtNiFe(111) surface and conclude that the coverage area of the {111} facets plays the key to guide the final shapes of PtNiFe nanocrystals in the alkyl phosphonic acid/oleylamine synthetic system. Further, the electrochemical results clearly demonstrate the structure-dependent oxygen reduction reaction activities of PtNiFe nanocatalysts in different electrolytes (HClO 4 and H 2 SO 4 ), which is valuable for the PtNiFe nanocatalysts in fuel cells.